Organic thin film transistor, method of manufacturing the same, and flat panel display device with the organic thin film transistor

ABSTRACT

An organic thin film transistor that has good adhesiveness and good contact resistance as well as allows ohmic contact between an organic semiconductor layer and a source electrode and a drain electrode, and its manufacturing method. There is also provided a flat panel display device using the organic thin film transistor. The organic thin film transistor includes a source electrode, a drain electrode, an organic semiconductor layer, a gate insulating layer, and a gate electrode formed on a substrate, and a carrier relay layer including conductive polymer material formed at least between the organic semiconductor layer and the source electrode or the organic semiconductor layer and the drain electrode.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from an applicationsearlier filed in the Korean Intellectual Property Office on 23 Nov.2004, 24 Oct. 2005, and 3 Nov. 2005 and there duly assigned Serial Nos.10-2004-0096210, 10-2005-0100278, and 10-2005-0104925, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic thin film transistor, amethod of manufacturing the same, and a flat panel display device withthe same, and more particularly, to an organic thin film transistor withan improved structure, a method of manufacturing the same, and a flatpanel display device with the same.

2. Description of the Related Art

Generally, a silicon thin film transistor includes a source region and adrain region doped with high-density impurities, a semiconductor layerhaving a channel region formed between the source region and the drainregion, a source electrode connected to the source region, and a drainelectrode connected to the drain region. Such silicon thin filmtransistor has disadvantages in that the manufacturing cost is high, andit can be easily broken by external impact, and it cannot be formed on aflexible plastic substrate because formation thereof requires a hightemperature process of over 300° C.

Unlike the silicon thin film transistor, an organic thin film transistor(OTFT) using an organic semiconductor layer can be formed on a plasticsubstrate, etc., because it can be manufactured at the room temperature.Since the organic thin film transistor can be used in various devicessuch as flexible display devices, smart cards, inventory tags, and pricetags, OTFTs are being vigorously developed. However, since the organicthin film transistor can not separately form a region doped with highdensity impurities, it has a disadvantage in that the contact resistancebetween an organic semiconductor layer and a source and drain electrodesis high.

In the meantime, the source electrode and the drain electrode of theorganic thin film transistor are made of noble metals such as gold (Au),platinum (Pt), palladium (Pd), etc. to form an ohmic contact. However,such noble metals for the source and drain electrodes are expensive. Inaddition, since their adhesiveness to the organic semiconductor layer ispoor, there is a high probability of failure and there is a short lifespan. Moreover, since such noble metals have very poor adhesiveness alsoto a gate insulating layer, a separate adhesive layer is additionallyrequired. What is needed is an improved design for an OTFT, and displayusing the same and an improved method of making that overcomes theseproblems.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved organic thin film transistor.

It is also an object of the present invention to provide a method ofmaking the organic thin film transistor.

It is further an object of the present invention to provide a displaythat employs the organic thin film transistor.

It is yet an object of the present invention to provide an organic thinfilm transistor which has good adhesiveness, good contact resistance aswell as allows ohmic contact between an organic semiconductor layer anda source electrode and a drain electrode, and a manufacturing methodthereof and a flat panel display device using the organic thin filmtransistor.

According to one aspect of the present invention, an organic thin filmtransistor includes a source electrode, a drain electrode, an organicsemiconductor layer, a gate insulating layer, a gate electrode and acarrier relay layer arranged at least between the organic semiconductorlayer and the source electrode or between the organic semiconductorlayer and the drain electrode, the carrier relay layer comprising aconductive polymer material.

The carrier relay layer can include a material selected from the groupconsisting of polyethylenedioxythiophene and polyaniline. The carrierrelay layer either has work function of between a work function of theorganic semiconductor layer and a work function of the source electrode,or has work function of between the work function of the organicsemiconductor layer and a work function of the drain electrode. Athickness of the carrier relay layer is in the range of 10 Å to 100 Å. Aresistivity of the carrier relay layer is in the range of 10⁵ Ωcm to10¹⁴ Ωcm. The carrier relay layer is arranged corresponding to at leastone of the source electrode and the drain electrode. The carrier relaylayer can be arranged on a top surface of at least one of the sourceelectrode and the drain electrode. The carrier relay layer can bearranged to cover an entire portion of an exposed surface of at leastone of the source electrode and the drain electrode.

The carrier relay layer can include a first carrier relay layer arrangedbetween the organic semiconductor layer and the source electrode, and asecond carrier relay layer arranged between the organic semiconductorlayer and the drain electrode, the first carrier relay layer and thesecond carrier relay layer being spaced apart from each other. Thecarrier relay layer arranged between the organic semiconductor layer andthe source electrode and the carrier relay layer arranged between theorganic semiconductor layer and the drain electrode can be integrallyformed. The carrier relay layer can be patterned to correspond to oneorganic thin film transistor. The source electrode or the drainelectrode can each include a material selected from the group consistingof Ti, Cr, Al and MoW.

The organic semiconductor layer includes at least one material selectedfrom the group consisting of pentacene, tetracene, anthracene,naphthalene, flullerene, alpha-6-thiophene, alpha-4-thiophene,oligothiophene, perylene and its derivative, rubrene and its derivative,coronene and its derivative, perylene tetracarboxylic diimide and itsderivative, perylene tetracarboxylic dianhydride and its derivative,polythiophene and its derivative, polyparaphenylenevinylene and itsderivative, polyparaphenylene and its derivative, polyfluorene and itsderivative, polythiophenevinylene and its derivative,polythiophene-heterocyclic aromatic copolymer and its derivative,oligoacene of naphthalene and its derivative, naphthalene tetracarboxylic acid diimide and its derivative, oligothiophene ofalpha-5-thiophene and its derivative, phthalocyanines with or withoutmetal and their derivatives, pyromellitic dianhydride and itsderivative, pyromellitic diimide and its derivative, polyalkylthiophene,polythienylenevinylene, alkylfluorene unit, and copolymer ofalkylthiophene.

The organic thin film transistor can also include a hydrophobic layerarranged at least between the organic semiconductor layer and the sourceelectrode or between the organic semiconductor layer and the drainelectrode. The carrier relay layer is arranged in a same layer as thehydrophobic layer, the carrier relay layer being adapted to fill inopenings in the hydrophobic layer. The carrier relay layer can include afirst carrier relay layer arranged between the organic semiconductorlayer and the source electrode, and a second carrier relay layerarranged between the organic semiconductor layer and the drainelectrode, the first carrier relay layer can be arranged to cover aportion of the source electrode closest to the drain electrode, thesecond carrier relay layer can be arranged to cover a portion of thedrain electrode closest to the source electrode.

The carrier relay layer can be arranged on a portion of a top surface ofat least one of the source electrode or the drain electrode. The carrierrelay layer can be arranged covering an entire portion of an exposedsurface of at least one of the source electrode and the drain electrode.The hydrophobic layer can include a surface treatment agent comprising aself-assembled monolayer having one to three of hydrophobic moiety, oneto three of reactive halogen atoms or alkoxy moiety, and silane moiety.The surface treatment agent of the hydrophobic layer can include ahydrophobic self-assembled monolayer having trichlorosilanyl moiety ortrialkoxysilanyl moiety at its terminal end. The hydrophobic layer mayinclude octadecyltrichlorosilane. The carrier relay layer can include amaterial selected from the group consisting ofpolyethylenedioxythiophene and polyaniline.

The present invention also contemplates a method of manufacturing anorganic thin film transistor, including forming a conductive polymermaterial layer on an entire surface of a substrate, and patterning theconductive polymer material layer by laser ablation technology to form acarrier relay layer, the carrier relay layer being arranged at leastbetween an organic semiconductor layer and a source electrode or betweenthe organic semiconductor layer and a drain electrode.

The present invention also contemplates a another method ofmanufacturing an organic thin film transistor, including forming ahydrophobic material layer on an entire surface of a substrate, formingan opening in the hydrophobic material layer and forming a carrier relaylayer in the opening, the carrier relay layer being arranged at leastbetween an organic semiconductor layer and a source electrode or betweenthe organic semiconductor layer and a drain electrode, the carrier relaylayer comprising a conductive polymer material. The hydrophobic materiallayer can be produced by a process selected from the group consisting ofspin coating and dipping. The opening in the hydrophobic material layercan be produced by a laser beam scanning process. The method further caninclude removing remaining conductive polymer material from between thesource electrode and the drain electrode after the forming the carrierrelay layer in the opening. The method can also include removingremaining conductive polymer material from between the source electrodeand the drain electrode and can be achieved by a process selected fromthe group consisting of laser beam, ultraviolet ray, or electron beamscanning.

The present invention also contemplates a flat panel display device thatincludes a substrate, and an organic thin film transistor arranged onthe substrate, the organic thin film transistor including a sourceelectrode, a drain electrode, an organic semiconductor layer, a gateinsulating layer, a gate electrode, and a carrier relay layer arrangedat least between the organic semiconductor layer and the sourceelectrode or between the organic semiconductor layer and the drainelectrode, the carrier relay layer comprises a conductive polymermaterial.

The carrier relay layer can include a material selected from the groupconsisting of polyethylenedioxythiophene and polyaniline. A thickness ofthe carrier relay layer is in the range of 10 Å to 100 Å. A resistivityof the carrier relay layer is in the range of 10⁵ Ωcm to 10¹⁴ Ωcm. Thedisplay device can also include a hydrophobic layer arranged at leastbetween the organic semiconductor layer and the source electrode orbetween the organic semiconductor layer and the drain electrode. Thecarrier relay layer is arranged on a same level as the hydrophobiclayer, the carrier relay layer being arranged in openings in thehydrophobic layer. The hydrophobic layer can include a surface treatmentagent having a self-assembled monolayer having one to three ofhydrophobic moiety, one to three of reactive halogen atoms or alkoxymoiety, and silane moiety. The surface treatment agent of thehydrophobic layer can include a hydrophobic self-assembled monolayerhaving trichlorosilanyl moiety or trialkoxysilanyl moiety at itsterminal end. The hydrophobic layer can includeoctadecyltrichlorosilane. The display device can also include an organiclight emitting device electrically connected to the organic thin filmtransistor, the organic light emitting device includes a firstelectrode, an organic light emitting layer, and a second electrode. Thedisplay device can include a plurality of organic thin film transistors,the carrier relay layer being integrally provided to the plurality oforganic thin film transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is a cross sectional view of an organic thin film transistoraccording to the first embodiment of the present invention;

FIG. 2 is a drawing illustrating energy barriers of an organic thin filmtransistor with a carrier relay layer;

FIG. 3 is an energy band diagram of an organic thin film transistor witha carrier relay layer;

FIG. 4 is a drawing illustrating an energy barrier of an organic thinfilm transistor without a carrier relay layer;

FIGS. 5 a to 5 d are cross sectional views of the organic thin filmtransistor to sequentially illustrate a manufacturing method of theorganic thin film transistor of FIG. 1;

FIG. 6 is a cross sectional view of an organic thin film transistoraccording to the first variation of the first embodiment of the presentinvention;

FIG. 7 is a cross sectional view of an organic thin film transistoraccording to the second variation of the first embodiment of the presentinvention;

FIG. 8 is a cross sectional view of an organic thin film transistoraccording to the third variation of the first embodiment of the presentinvention;

FIG. 9 is a cross sectional view of an organic thin film transistoraccording to the fourth variation of the first embodiment of the presentinvention;

FIG. 10 is a schematic cross sectional view of a flat panel displaydevice according to the first embodiment of the present inventionemploying the organic thin film transistor of FIG. 9;

FIG. 11 is a cross sectional view of an organic thin film transistoraccording to the second embodiment of the present invention;

FIGS. 12 a to 12 d are cross sectional views of the organic thin filmtransistor to sequentially illustrate a manufacturing method of theorganic thin film transistor of FIG. 11;

FIG. 13 is a cross sectional view of an organic thin film transistoraccording to the first variation of the second embodiment of the presentinvention;

FIG. 14 is a cross sectional view of an organic thin film transistoraccording to the second variation of the second embodiment of thepresent invention;

FIG. 15 is a cross sectional view of an organic thin film transistoraccording to the third variation of the second embodiment of the presentinvention;

FIG. 16 is a cross sectional view of an organic thin film transistoraccording to the fourth variation of the second embodiment of thepresent invention;

FIGS. 17 a to 17 d are cross sectional views of the organic thin filmtransistor to sequentially illustrate a manufacturing method of theorganic thin film transistor of FIG. 16; and

FIG. 18 is a schematic cross sectional view of a flat panel displaydevice according to the second embodiment of the present inventionemploying the organic thin film transistor of FIG. 16.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the figures, FIG. 1 is a cross sectional view of anorganic thin film transistor according to the first embodiment of thepresent invention. As shown in FIG. 1, a source electrode 21 a and adrain electrode 21 b are formed on a substrate 20, and carrier relaylayers 23 a and 23 b and an organic semiconductor layer 26 aresequentially formed covering the source electrode 21 a and the drainelectrode 21 b. Accordingly, the carrier relay layers 23 a and 23 b arelocated between the source and drain electrodes 21 a and 21 b and theorganic semiconductor layer 26. A gate insulating layer 27 is formedcovering the organic semiconductor layer 26, and a gate electrode 29 isformed on the gate insulating layer 27 between the source and drainelectrodes 21 a and 21 b.

The details of the organic thin film transistor of FIG. 1 are asfollows. The substrate 20 can be made of glass, silicon, plastic, ormetal. The plastic can be polyethylene terephthalate (PET), polyethylenenaphtahlate (PEN), polyether sulfone (PES), polyether imide,polyphenylene sulfide (PPS), polyallyate, polyimide, polycarbonate (PC),cellulose triacetate, cellulose acetate propionate (CAP), etc.

The source electrode 21 a and the drain electrode 21 b can be made ofmetal with the different work function from that of organicsemiconductor layer 26. For example, if the organic semiconductor layer26 is p-type, it is made of material with work function of 5.0 eV ormore. Accordingly, the source electrode 21 a and the drain electrode 21b can be made of metal with work function of less than 5.0 eV, and ispreferably made out of either Ti, Cr, Al or MoW.

Alternatively, the source electrode 21 a and the drain electrode 21 bcan be made of transparent material such as indium tin oxide (ITO),indium zinc oxide (IZO), ZnO or In₂O₃, etc. This is because when theorganic thin film transistor is electrically connected to a transparentpixel electrode (not shown in the drawing) of a flat display paneldevice described below, it allows the pixel electrode and the source anddrain electrodes 21 a and 21 b to be integrally formed. Then, the reasonwhy the pixel electrode is transparent is to transmit generated light.

The carrier relay layers 23 a and 23 b are made of material having workfunction between that of the organic semiconductor layer 26 and that ofthe source and drain electrodes 21 a and 21 b. Such carrier relay layers23 a and 23 b separate the energy barrier between the organicsemiconductor layer 26 and the source and drain electrodes 21 a and 21 binto smaller energy barriers. A cascade effect in accordance therewithfacilitates hole injection from the source and drain electrodes 21 a and21 b into the organic semiconductor layer 26 to thus form an ohmiccontact.

Turning now to FIGS. 2 through 4, FIG. 2 shows energy barriers of anorganic thin film transistor having a carrier relay layer with workfunction of 5.0 eV formed between the p-type organic semiconductor layerhaving a work function of 5.3 eV and the source and drain electrodes(for example, made of MoW) with a work function of 4.6 eV. In addition,FIG. 3 shows an energy band diagram of such organic thin film transistorand FIG. 4 shows energy barrier of an organic thin film transistorhaving the same structure as that of the above organic thin filmtransistor but without the carrier relay layer.

When a carrier relay layer is present, the relatively greater energybarrier (BL3) between the organic semiconductor layer and the source anddrain electrodes shown in FIG. 4 is separated into the smaller energybarriers (BL1 and BL2) as illustrated in FIG. 2. Accordingly, as shownin FIG. 3, the organic thin film transistor having the carrier relaylayer present can induce a cascade effect.

The carrier relay layers 23 a and 23 b can be made of conductive polymermaterial such as polyethylene dioxythiophene (PEDOT), polyaniline(PANI), etc. However, the present invention is not limited to the aboveand the carrier relay layer can be made of various other materials andstill be within the scope of the present invention. In the presentembodiment of FIG. 1, the carrier relay layers 23 a and 23 b made of aconductive polymer material are provided between the organicsemiconductor layer 26 and each of the source electrode 21 a and thedrain electrode 21 b to reduce contact resistance. In addition, sincethe carrier relay layers 23 a and 23 b of conductive polymer materialare located between the source electrode 21 a and the drain electrode 21b of inorganic material and the organic semiconductor layer 26 oforganic material, the adhesiveness between the organic semiconductorlayer 26 and the source electrode 21 a and the drain electrode 21 b isimproved. It is preferable that the carrier relay layers 23 a and 23 bhave a thickness of 10 Å to 100 Å and that they have a resistivity of10⁵ Ωcm to 10¹⁴ Ωcm.

Because the carrier relay layers 23 a and 23 b are located between thesource and drain electrodes 21 a and 21 b and the organic semiconductorlayer 26, the carrier relay layers 23 a and 23 b determine the distancebetween the organic semiconductor layer 26 and each of the source anddrain electrodes 21 a and 21 b. If the thickness of the carrier relaylayers 23 a and 23 b is greater than 100 Å, since the distance betweenthe source and drain electrodes 21 a and 21 b and the organicsemiconductor layer 26 becomes great, there is a problem in thatelectrical conduction between them is not effective. If the thickness ofthe carrier relay layers 23 a and 23 b is less than 10 Å, there is aproblem in that the carrier relay layers 23 a and 23 b can not properlyfunction and they are not stably formed.

As the organic thin film transistor functions as a switching device or adriving device, a channel in the organic semiconductor layer 26 shouldbe formed to communicate electric signals between the source electrode21 a and the drain electrode 21 b only when a predetermined electricalsignal is applied to the gate electrode 29. However, if the resistivityof the carrier relay layers 23 a and 23 b is less than 10⁵ Ωcm, when thecarrier relay layer is integrally formed in the organic thin filmtransistor (see the first variation of the present embodiment), theelectrical signal can be communicated between the source electrode andthe drain electrode even though a channel is not formed in the organicsemiconductor layer. That is, in the present invention, the resistivityof the carrier relay layers 23 a and 23 b should be equal to or greaterthan 10⁵ Ωcm so that electrical signals are not communicated between thesource electrode 21 a to the drain electrode 21 b regardless of theshape of the carrier relay layers 23 a and 23 b. The details thereofwill be further explained in the first variation of the presentembodiment of FIG. 6. On the other hand, if the resistivity of thecarrier relay layer 23 a and 23 b is greater than 10¹⁴ Ωcm, theelectrical conduction from the source electrode 21 a and the drainelectrode 21 b to the organic semiconductor layer 26 is not effective.

Accordingly, the range of the resistivity of the carrier relay layers 23a and 23 b is within a range where the electrical conduction from thesource electrode 21 a to the drain electrode 21 b does not occur whenthe transistor is turned off but the electrical conduction from thesource electrode 21 a and the drain electrode 21 b via the organicsemiconductor layer 26 readily occurs when the transistor is turned on.

In the present embodiment, the carrier relay layers 23 a and 23 b arepatterned to correspond to one organic thin film transistor. That is, ifa plurality of organic thin film transistors are provided, the carrierrelay layers 23 a and 23 b of different transistors are separate fromeach other.

The carrier relay layers 23 a and 23 b can include a first carrier relaylayer 23 a located between the source electrode 21 a and the organicsemiconductor layer 26, and a second carrier relay layer 23 b locatedbetween the drain electrode 21 b and the organic semiconductor layer 26.The first carrier relay layer 23 a is formed covering the entire portionof the exposed surface of the source electrode 21 a, and the secondcarrier relay layer 23 b is formed covering the entire portion of theexposed surface of the drain electrode 21 b. Accordingly, the firstcarrier relay layer 23 a and the second carrier relay layer 23 b arespaced apart from each other.

In addition, the organic semiconductor layer 26 is a region where achannel is formed within when the transistor is turned on. If aplurality of organic thin film transistors are provided, the organicsemiconductor layer 26 is patterned separately for each organic thinfilm transistor unit to prevent crosstalk between the adjacent thin filmtransistors. That is, the organic semiconductor layer 26 is insulatedfrom the adjacent organic semiconductor layers (not shown).

The organic semiconductor layer 26 can be made of pentacene, tetracene,anthracene, naphthalene, flullerene, alpha-6-thiophene,alpha-4-thiophene, oligothiophene, perylene and its derivative, rubreneand its derivative, coronene and its derivative, perylenetetracarboxylic diimide and its derivative, perylene tetracarboxylicdianhydride and its derivative, polythiophene and its derivative,polyparaphenylenevinylene and its derivative, polyparaphenylene and itsderivative, polyfluorene and its derivative, polythiophenevinylene andits derivative, polythiophene-heterocyclic aromatic copolymer and itsderivative, oligoacene of naphthalene and its derivative, naphthalenetetra carboxylic acid diimide and its derivative, oligothiophene ofalpha-5-thiophene and its derivative, phthalocyanines with or withoutmetal and their derivatives, pyromellitic dianhydride and itsderivative, pyromellitic diimide and its derivative, polyalkylthiophene,polythienylenevinylene, alkylfluorene unit, copolymer of alkylthiophene,etc. In the present embodiment, the organic semiconductor layer 26 canbe made of p-type organic semiconductor material. However, the presentinvention is not limited thereto.

The gate insulating layer 27 can be made of an organic material such asbenzocyclobutene (BCB), polyimide, polyvinylphenol, parylene, epoxy,polyvinyl chloride, CYPE, etc. In addition, the gate electrode 29 can bemade of conductive metal such as MoW, Al, Cr, Al/Cr, etc., or aconductive polymer.

Turning now to FIGS. 5 a to 5 d, a manufacturing method of the organicthin film transistor of FIG. 1 will now be described. As the materialfor each element is the same as described above, the explanation of thesame or similar elements will be omitted unless necessary. FIGS. 5 a to5 d are cross sectional views of the organic thin film transistor tosequentially illustrate a manufacturing method thereof according to thefirst embodiment of the present invention.

As shown in FIG. 5 a, the source electrode 21 a and the drain electrode21 b are formed on the substrate 20. The source electrode 21 a and thedrain electrode 21 b can be formed by vapor depositing on the entiresurface of the substrate 20 to form a conductive material layer andpatterning the conductive material layer. Alternatively, the sourceelectrode 21 a and the drain electrode 21 b can be formed by forming theconductive material layer in a predetermined pattern of the substrate 20using a mask. Alternatively, the source and drain electrodes 21 a and 21b can be formed by inkjet printing, etc.

As shown in FIG. 5 b, the first and the second carrier relay layers 23 aand 23 b are formed covering the entire portion of the exposed surfaceof the source electrode 21 a and the drain electrode 21 b. The first andthe second carrier relay layers 23 a and 23 b can be formed by formingconductive polymer material layer of polyethylenedioxythiophene,polyaniline, etc. on the entire surface of the substrate 20 using spincoating, dipping or inkjet printing. The conductive polymer layer isthen patterned using laser ablation technology (LAT). However, thepresent invention is not limited thereto.

Turning now to FIG. 5 c, the organic semiconductor material layer isvapor deposited on the entire surface of the substrate 20 to cover thecarrier relay layers 23 a and 23 b. The organic semiconductor materiallayer is then patterned for each organic thin film transistor unit toform the organic semiconductor layer 26. The organic semiconductormaterial layer formed on the entire surface of the substrate 20 can bepatterned by laser ablation technology. However, the present inventionis not limited thereto.

Turning now to FIG. 5 d, the gate insulating layer 27 is formed bycoating organic insulating material on the entire surface of thesubstrate 20. A gate electrode 29 is then formed on the gate insulatinglayer 27. The gate electrode 29 can be formed by vapor depositing on theentire surface of the substrate 20 to form a conductive layer, and thenpatterning it. Alternatively, the gate electrode 29 can be formed byforming the conductive material layer in a predetermined pattern of thesubstrate 20 using a mask. Alternatively, the gate electrode 29 can beformed by inkjet printing, etc.

Although it is described in the above that the carrier relay layers 23 aand 23 b are formed to cover an entire portion of the exposed surface ofthe source and drain electrodes 21 a and 21 b, the present invention isnot limited thereto as the carrier relay layers 23 a and 23 b can bemodified in various ways. Such variations will be described in detailwith reference to FIGS. 6 to 9.

As the variations have the same basic structure as the organic thin filmtransistor of FIG. 1, the illustration of the same or similar elementswill be omitted. That is, since the material and characteristics foreach element have already been discussed above in conjunction with FIG.1, the illustration thereof will be omitted when describing thesevariations of the organic thin film transistor of FIG. 1.

Turning now to FIG. 6, FIG. 6 is a cross sectional view of an organicthin film transistor according to the first variation of the firstembodiment of the present invention. With reference to FIG. 6, thecarrier relay layer 33 is integrally formed on the substrate 30 betweenthe source electrode 31 a and the organic semiconductor layer 36, andbetween the drain electrode 31 b and the organic semiconductor layer 36.The gate insulating layer 37 is formed covering the organicsemiconductor layer 36, and the gate electrode 39 is formed thereon.

Then, although the carrier relay layer 33 is integrally formed, sincethe resistivity of the carrier relay layer 33 is equal to or greaterthan 10⁵ Ωcm, the problem of the electrical conduction from the sourceelectrode 31 a to the drain electrode 31 b when the organic thin filmtransistor is turned off does not occur. Since the thickness of thecarrier relay layer 33 is less than 100 Å, the distance between theorganic semiconductor layer 36 and each of the source electrode 31 a andthe drain electrode 31 b is small enough so that electrical conductionthrough carrier relay layer 33 readily occurs. In contrast, since thedistance between the source electrode 31 a and the drain electrode 31 bis relatively large compared to the distance between the organicsemiconductor layer 36 and each of the source and drain electrodes 31 aand 31 b and since the resistivity of the carrier relay layer 33 is atleast 10⁵ Ωcm, the electrical conduction from the source electrode 31 ato the drain electrode 31 b does not occur when the organic thin filmtransistor is switched off.

In the organic thin film transistor of FIG. 6, it is possible that thecarrier relay layer 33 is independently patterned for each of aplurality of the organic thin film transistors, or instead the carrierrelay layer 33 can be integrally provided for a plurality of the organicthin film transistors. In the latter case, since the patterning processis omitted, the manufacturing process has an advantage in that themanufacturing process can be simplified.

Turning now to FIG. 7, FIG. 7 is a cross sectional view of an organicthin film transistor according to the second variation of the firstembodiment of the present invention. With reference to FIG. 7, the firstand second carrier relay layers 43 a and 43 b are formed only on the topsurface of the source electrode 41 a and the drain electrode 41 b on thesubstrate 40, respectively. The organic semiconductor layer 46 and thegate insulating layer 47 are sequentially formed covering the carrierrelay layers 43 a and 43 b, the substrate 40 and the edge portions ofthe source and drain electrodes 41 a and 41 b. The gate electrode 49 isthen formed on the gate insulating layer 47.

Turning now to FIG. 8, FIG. 8 is a cross sectional view of an organicthin film transistor according to the third variation of the firstembodiment of the present invention. With reference to FIG. 8, the gateelectrode 59 is formed on the substrate 50 below the source and drainelectrodes 51 a and 51 b, the carrier relay layer 53, the organicsemiconductor layer 56 and the gate insulating layer 57. The gateinsulating layer 57 is interposed between the gate electrode 59 and thesource and drain electrodes 51 a and 51 b. Then, the source electrode 51a and the drain electrode 51 b are formed below the organicsemiconductor layer 56 and below the carrier relay layer 53. The carrierrelay layer 53 is formed between the organic semiconductor layer 56 andthe source and drain electrodes 51 a and 51 b.

In the present variation of FIG. 8, the gate insulating layer 57contacts both the source and drain electrodes 51 a and 51 b. The sourceand drain electrodes 51 a and 51 b are made of one or more of Ti, Cr,Al, MoW, ITO, IZO, ZnO, In₂O₃, etc, each of which have good adhesivenessto the gate insulating layer 57. Accordingly, a separate adhesive layeris not needed between the gate insulating layer 57 and the source anddrain electrodes 51 a and 51 b, thus simplifying the manufacturingprocess while avoiding the problem of deteriorating contact resistancecaused by an adhesive layer.

Turning now to FIG. 9, FIG. 9 is a cross sectional view of an organicthin film transistor according to the fourth variation of the firstembodiment of the present invention. With reference to FIG. 9, the gateelectrode 69 is formed on the substrate 60 below the organicsemiconductor layer 66, the carrier relay layer 63, and the source anddrain electrodes 61 a and 61 b. A gate insulating layer 67 is interposedbetween the gate electrode 69 and each of the organic semiconductorlayer 66, the carrier relay layer 63, and the source and drainelectrodes 61 a and 61 b. The source electrode 61 a and the drainelectrode 61 b are formed on carrier relay layer 63 which is formed onthe organic semiconductor layer 66. The carrier relay layer 63 is formedbetween the organic semiconductor layer 66 and the source and drainelectrodes 61 a and 61 b.

The manufacturing method of the organic thin film transistor accordingto the above variations is substantially the same as that of the organicthin film transistor according to the first embodiment, and is differentonly in its sequence and whether or not a layer is patterned, so theexplanation thereof will omitted. In the meantime, the organic thin filmtransistor of the present invention described above can be used for aflat panel display device like an organic light emitting display device,etc., the details of which will be described in the following withreference to FIG. 10.

FIG. 10 is a schematic cross sectional view of a flat panel displaydevice according to the first embodiment of the present invention. Asshown in FIG. 10, the organic thin film transistor (TFT1) is formed onthe substrate 70. Although FIG. 10 shows the organic thin filmtransistor (TFT1) according to the fourth variation of FIG. 9, thepresent invention is not limited thereto.

As illustrated in FIG. 10, a passivation layer 73 made of SiO₂, etc. isformed on the organic thin film transistor (TFT1), and a pixel defininglayer 75 made of acryl, polyimide, etc. is formed on the passivationlayer 73. The passivation layer 73 can function as a protection layerfor protecting the organic thin film transistor (TFT1), and it can alsofunction as a flattening layer for flattening its top surface.

In addition, although not shown in FIG. 10, at least one capacitor canbe connected to the organic thin film transistor (TFT1). Furthermore, acircuit including such organic thin film transistor (TFT1) is notlimited only to the embodiment shown in FIG. 10, and it can be modifiedin various ways.

In FIG. 10, the drain electrode 61 b is connected to a light emittingdevice 80 through a via hole 73 a formed in the passivation layer 73.The light emitting device 80 includes a pixel electrode 81 and anopposite electrode 85 facing each other, and an intermediate layer 83interposed between the pixel electrode 81 and the opposite electrode 85,the intermediate layer 83 having at least a light emitting layer. Theopposite electrode 85 can be formed commonly with respect to a pluralityof sub-pixels, and it can be modified in various ways.

Although FIG. 10 shows that the intermediate layer 83 is patterned tocorrespond only to the sub pixel, this illustration is for theconvenience in explanation of the structure of the sub pixel. Theintermediate layer 83 can instead be integrally formed with theintermediate layer of the adjacent sub pixel. In addition, theintermediate layer 83 can be modified in various ways such that somelayer of the intermediate layer 83 is independently formed in each subpixel, and the other layer is integrally formed with the intermediatelayer of the adjacent sub pixel.

In FIG. 10, the pixel electrode 81 functions as an anode electrode, andthe opposite electrode 85 functions as a cathode electrode. However, thepolarity of the pixel electrode 81 and the opposite electrode 85 can bereversed. In addition, since the pixel electrode 81 and the drainelectrode 61 b are electrically connected to each other, they can beintegrally formed.

The pixel electrode 81 can be provided as a transparent electrode or areflection type electrode. If the pixel electrode 81 is a transparentelectrode, it can be made of ITO, IZO, ZnO or In₂O₃. If the pixelelectrode 81 is a reflection type electrode, it can include a firstlayer made of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr or their mixture,and a second layer made of ITO, IZO, ZnO, In₂O₃, etc. and formed on thefirst layer.

The opposite electrode 85 can be also provided as a transparentelectrode or a reflection type electrode. If the opposite electrode 85is a transparent electrode, it can include a first layer made of Li, Ca,LiF/Ca, LiF/Al, Al, Mg, or a mixture thereof, and a second layer made ofITO, IZO, ZnO, In₂O₃, etc. and formed on the first layer. The secondlayer is formed as an auxiliary electrode or a bus electrode line.Alternatively, if the opposite electrode 85 is a reflection typeelectrode, it can be formed by vapor depositing Li, Ca, LiF/Ca, LiF/Al,Al, Mg, or their mixture on the entire surface.

The intermediate layer 83 located between the pixel electrode 81 and theopposite electrode 85 can include low molecular organic material or highmolecular organic material. If the intermediate layer 83 is a lowmolecular organic material, it is formed by stacking a hole injectionlayer (HIL), a hole transport layer (HTL), an emission layer (EML), anelectron transport layer (ETL), an electron injection layer (EIL), etc.in a single structure or in a composite structure. Copper phthalocyanine(CuPc), N,N′-Di(naphthalene-1-yl)— N,N′-diphenyl-benzidine (NPB),tris-8-hydroxyquinoline aluminum (Alq3), or the like can be used as theorganic material. Such low molecular organic material can be formed byvapor depositing using masks.

If the intermediate layer 83 is a high molecular organic material, itgenerally has a hole transport layer (HTL) and an emission layer (EML).The hole transport layer (HTL) can include polyethylenedioxythiophene,and the emission layer (EML) can include polyphenylenevinylene type orpolyfluorene type material.

Although the above discussion pertains to an organic light emittingdisplay device, the present invention is not limited thereto, and thepresent invention can also apply to other flat panel display devicessuch as a liquid crystal display device, etc. In other words, thevarious designs for organic thin film transistors discussed inconjunction with FIGS. 1 and 6 through 9 can apply to other types ofdisplays besides organic light emitting display devices and still bewithin the scope of the present invention. Since the organic thin filmtransistors described above can be manufactured in a flexible form, itcan be used in various flat panel display devices to provide flexiblecharacteristics. In particular, it is more useful when the material usedfor the flat panel display device is an organic material.

In the following, the organic thin film transistors and theirmanufacturing methods according to the second embodiment of the presentinvention and its variations will now be described. Turning now to FIG.11, FIG. 11 is a cross sectional view of an organic thin film transistoraccording to the second embodiment of the present invention. As shown inFIG. 11, a source electrode 121 a and a drain electrode 121 b are formedon a substrate 120, and carrier relay layers 123 a and 123 b and ahydrophobic layer 124 are formed covering the source electrode 121 a andthe drain electrode 121 b, and an organic semiconductor layer 126 isformed thereon. A gate insulating layer 127 is formed covering theorganic semiconductor layer 126, and a gate electrode 129 is formed onthe gate insulating layer 127 between the source electrode 121 a and thedrain electrode 121 b.

The carrier relay layers 123 a and 123 b are formed on the same level asthe hydrophobic layer 124 and fill in openings in the hydrophobic layer124. In the present embodiment of FIG. 11, a first carrier relay layer123 a is formed on a portion of the top surface of the source electrode121 a between the organic semiconductor layer 126 and the sourceelectrode 121 a, and a second carrier relay layer 123 b is formed on aportion of the top surface of the drain electrode 121 b between theorganic semiconductor layer 126 and the drain electrode 121 b.

More specifically, in FIG. 11, the hydrophobic layer 124 has openings124 a and 124 b corresponding to the top middle portion of the sourceelectrode 121 a and the drain electrode 121 b, respectively, and thefirst and the second carrier relay layers 123 a and 123 b are formed ineach of the openings 124 a and 124 b, respectively. That is, the firstand the second carrier relay layers 123 a and 123 b are formed in themiddle of the top surfaces of the source electrode 121 a and the drainelectrode 121 b, respectively.

Then, it is preferable that conductive polymer material for the carrierrelay layers 123 a and 123 b is not located between the source electrode121 a and the drain electrode 121 b, considering a channel is formedbetween the source electrode 121 a and the drain electrode 121 b.Accordingly, in the present embodiment, the first and the second carrierrelay layers 123 a and 123 b are formed on a portion of the top surfaceof the source electrode 121 a and the drain electrode 121 b,respectively.

The hydrophobic layer 124 can include a surface treatment agentcontaining a self-assembled monolayer having one to three of hydrophobicmoiety, one to three of reactive halogen atoms or alkoxy moiety, andsilane moiety. In particular, it is preferable that the hydrophobiclayer 124 includes a surface treatment agent containing a hydrophobicself-assembled monolayer having trichlorosilanyl moiety ortrialkoxysilanyl moiety at its terminal end. Such material can beoctadecyltrichlorosilane (OTC), etc.

In FIG. 11, the material for the substrate 120, the source electrode 121a, the drain electrode 121 b, the first and the second carrier relaylayers 123 a and 123 b, the organic semiconductor layer 126, the gateinsulating layer 127 and the gate electrode 129 is the same as that ofthe elements corresponding to the first embodiment of FIGS. 1 and 6through 9, and thus the details thereof will be omitted.

In the present embodiment of FIG. 11, since the first and the secondcarrier relay layers 123 a and 123 b are present, the organicsemiconductor layer 126 and the source electrode 121 a and the drainelectrode 121 b have an ohmic contact, and the contact resistancebetween the organic semiconductor layer 126 and the source electrode 121a and the drain electrode 121 b can be reduced. The carrier relay layers123 a and 123 b also enhance adhesiveness between the organicsemiconductor layer 126 and each of the source electrode 121 a and thedrain electrode 121 b.

In addition, in the present embodiment of FIG. 11, since the hydrophobiclayer 124 is present, the carrier relay layers 123 a and 123 b can beformed only between the source electrode 121 a and the organicsemiconductor layer 126 and between the drain electrode 121 b and theorganic semiconductor layer 126. Accordingly, the hydrophobic layer 124substantially prevents communicating unwanted electric signals betweenthe source electrode 121 a and the drain electrode 121 b when theorganic thin film transistor is turned off.

Turning now to FIGS. 12 a to 12 d, a manufacturing method of suchorganic thin film transistor of FIG. 11 will now be described. As thematerial for each element is the same as discussed in conjunction withFIG. 11, the explanation thereof will be omitted.

FIGS. 12 a to 12 d are cross sectional views of the organic thin filmtransistor to sequentially illustrate a manufacturing method thereofaccording to the second embodiment of the present invention. As shown inFIG. 12 a, the source electrode 121 a and the drain electrode 121 b areformed on the substrate 120. A hydrophobic material layer 124 c isformed on the entire surface of the substrate 120 to cover the sourceelectrode 121 a and the drain electrode 121 b.

The source electrode 121 a and the drain electrode 121 b can be formedby vapor depositing on the entire surface of the substrate 120 to form aconductive layer and then patterning the conductive layer.Alternatively, the source electrode 121 a and the drain electrode 121 bcan be formed by forming a patterned conductive layer on the substrate120 using a mask. Alternatively, source electrode 121 a and drainelectrode 121 b can be formed by inkjet printing, etc.

In addition, the hydrophobic material layer 124 c can be formed byapplying hydrophobic material on the entire surface of the substrate 120using spin coating, dipping, etc. Then, as shown in FIG. 12 b, thehydrophobic material layer 124 c is patterned to become hydrophobiclayer 124 by removing a portion of the hydrophobic material layer (124 cin FIG. 12 a) to expose a portion of the top surface of the sourceelectrode 121 a and a portion of the top surface of the drain electrode121 b. For example, in FIG. 12 b, a laser beam is scanned to a portionof the hydrophobic material layer 124 c using a mask 220 to formopenings 124 a and 124 b. However, the present invention is not limitedthereto. The mask 220, for example, has shielding material 223 in theform of a pattern to block the laser beam formed with the pattern on atransparent plate 221.

Then, as shown in FIG. 12 c, the first and the second carrier relaylayers 123 a and 123 b are formed by forming conductive polymer materiallayers to fill the openings 124 a and 124 b of the hydrophobic layer124. Due to the characteristics of the hydrophobic layer 124, conductivepolymer material layer cannot be formed on the hydrophobic layer 124,and accordingly, the first and the second carrier relay layers 123 a and123 b are readily formed only in the openings 124 a and 124 b of thehydrophobic layer 124 without having to separately pattern theconductive polymer material in a separate process step. The first andthe second carrier relay layers 123 a and 123 b can be formed by variousmethods, such as by inkjet printing, etc. In particular, dipping or spincoating processes are preferable because they can simplify themanufacturing process and shorten manufacturing time.

After completing the organic thin film transistor, a channel is formedbetween the source electrode 121 a and the drain electrode 121 b whenthe transistor is turned on. It is preferable that the conductivepolymer material not be present between the source electrode 121 a andthe drain electrode 121 b when the carrier relay layers 123 a and 123 bof the conductive polymer material layer are formed. When thehydrophobic layer 124 is present and the carrier relay layers 123 a and123 b are, in general, not formed between the source electrode 121 a andthe drain electrode 121 b. However, it is still possible that a smallamount of the conductive polymer material can be remained despite thepresence of hydrophobic layer 124. To remove this, a step of removingthe conductive polymer material remaining between the source electrode121 a and the drain electrode 121 b can be carried out in addition tothe above steps. Removal of the unwanted conductive polymer material canbe carried out, for example, by scanning laser beam, ultraviolet ray, orelectron beam in the region between the source electrode 121 a and thedrain electrode 121 b.

Then, as shown in FIG. 12 d, the organic semiconductor layer 126 isformed, the gate insulating layer 127 is formed to cover the organicsemiconductor layer 126, and the gate electrode 129 is formed on thegate insulating layer 127 to complete the organic thin film transistorof FIG. 11. The organic semiconductor layer 126 can be formed by variousmethods such as by inkjet printing, dipping, spin coating, etc. Themanufacturing method of the organic thin film transistor according toFIGS. 12 a through 12 d has advantages in that it enables the carrierrelay layers 123 a and 123 b to be readily formed, and accordingly, theorganic thin film transistor of high quality can be manufactured withlow cost.

Turning now to FIG. 13, FIG. 13 is a cross sectional view of an organicthin film transistor according to the first variation of the secondembodiment of the present invention. As illustrated in FIG. 13, thefirst carrier relay layer 133 a, located on a top surface of sourceelectrode 131 a, is formed on a portion of the top surface of sourceelectrode 131 a closest to the drain electrode 131 b. Similarly, thesecond carrier relay layer 133 b is located on a portion of the topsurface of drain electrode 131 b closest to source electrode 131 a. Thispositioning is accomplished by forming opening 134 a in the hydrophobiclayer 134 on the source electrode 131 a at an side of the top surface ofsource electrode 131 a closest to drain electrode 131 b. Likewise,opening 134 b of the hydrophobic layer 134 formed on a side of the topsurface of drain electrode 131 b closest to the source electrode 131 a.The first and the second carrier relay layers 133 a and 133 b are formedto fill these openings 134 a and 134 b.

Between the source electrode 131 a and the drain electrode 131 b, anelectric signal is communicated through the channel formed in theorganic semiconductor layer 136 according to a predetermined electricsignal applied to the gate electrode 139. Considering this, the presentembodiment forms the first and the second carrier relay layers 133 a and133 b, which can facilitate transmitting the electric signals. Then, itis preferable that the source electrode 131 a and the drain electrode131 b are electrically communicated with each other through the firstand the second carrier relay layers 133 a and 133 b on the sourceelectrode 131 a and the drain electrode 131 b when the transistor isturned on. The reference numeral 137 in FIG. 13 is the gate insulatinglayer.

Turning now to FIG. 14, FIG. 14 is a cross sectional view of an organicthin film transistor according to the second variation of the secondembodiment of the present invention. With reference to FIG. 14, thefirst carrier relay layer 143 a is formed to cover the end or sidewallsurface of the source electrode 141 a that faces drain electrode 141 b,and the second carrier relay layer 143 b is formed to cover the end orsidewall surface of the drain electrode 141 b that faces sourceelectrode 141 a. Accordingly, the electric signal between the sourceelectrode 141 a and the drain electrode 141 b can be communicatedthrough the first and the second carrier relay layers 143 a and 143 b.The organic semiconductor layer 146, the gate insulating layer 147 andthe gate electrode 149 are sequentially formed on the carrier relaylayers 143 a and 143 b.

Turning now to FIG. 15, FIG. 15 is a cross sectional view of an organicthin film transistor according to the third variation of the secondembodiment of the present invention. With reference to FIG. 15, thefirst and the second carrier relay layers 153 a and 153 b are formed tocover the entire top and side surfaces of the source electrode 151 a andthe drain electrode 151 b respectively. The first and the second carrierrelay layers 153 a and 153 b are formed in openings in the hydrophobiclayer 154. The organic semiconductor layer 156, the gate insulatinglayer 157 and the gate electrode 159 are sequentially formed on thecarrier relay layers 153 a and 153 b.

The manufacturing method of the organic thin film transistor accordingto the first to the third variations of the second embodiment (FIGS. 13through 15) is substantially the same as that of the organic thin filmtransistor according to the non-variant version of the second embodiment(FIGS. 11 through 12 d), and is different only in the location where theopening in the hydrophobic layer is formed, so the explanation thereofis omitted.

Turning now to FIG. 16, FIG. 16 is a cross sectional view of an organicthin film transistor according to the fourth variation of the secondembodiment of the present invention. With reference to FIG. 16, the gateelectrode 169 formed on the substrate 160 and is formed below the sourceelectrode 161 a, the drain electrode 161 b, the carrier relay layers 163a and 163 b, the hydrophobic layer 164, and the organic semiconductorlayer 166, and the gate insulating layer 167. Gate insulating layer 167is formed between the gate electrode 169 and the source electrode 161 a,the drain electrode 161 b, the carrier relay layers 163 a and 163 b, thehydrophobic layer 164, and the organic semiconductor layer 166. Thesource electrode 161 a and the drain electrode 161 b are formed belowthe organic semiconductor layer 166. The carrier relay layers 163 a and163 b are formed between the organic semiconductor layer 166 and thesource electrode 161 a and the drain electrode 161 b.

In FIG. 16, the source and drain electrodes 161 a and 161 b and the gateinsulating layer 167 contact each other, and the source and drainelectrodes 161 a and 161 b are made of Ti, Cr, Al, MoW, ITO, IZO, ZnO,In₂O₃, etc. which have good adhesiveness to the gate insulating layer167. Accordingly, a separate adhesive layer is not needed between thegate insulating layer 167 and the source and drain electrodes 161 a and161 b, resulting in a simplified and less expensive method of makingwhile preventing deterioration of contact resistance characteristicscaused by the presence of an adhesive layer.

Turning now to FIGS. 17 a to 17 d, a manufacturing method of the organicthin film transistor of FIG. 16 will now be described. As the materialfor each element is the same as the above, the explanation thereof willbe omitted.

FIGS. 17 a to 17 d are cross sectional views of the organic thin filmtransistor to sequentially illustrate a manufacturing method thereofaccording to the fourth variation of the second embodiment of thepresent invention. As shown in FIG. 17 a, the gate electrode 169, thegate insulating layer 167, the source electrode 161 a and the drainelectrode 161 b are sequentially formed on the substrate 160. Thehydrophobic material layer 164 c is formed on the entire surface of thesubstrate 160 to cover the source electrode 161 a and the drainelectrode 161 b.

Then, as shown in FIG. 17 b, a portion of the hydrophobic material layer(164 c in FIG. 17 a) is removed by various ways such as scanning laserbeam with a mask 240, etc. to expose a portion of the top surface ofeach of the source electrode 161 a and the drain electrode 161 b.Accordingly, the hydrophobic layer 164 is formed to have openings 164 aand 164 b exposing a portion of the top surface of the source electrode161 a and a portion of the top surface of the drain electrode 161 b.Then, as shown in FIG. 17 c, the first and the second carrier relaylayers 163 a and 163 b are formed to fill the openings 164 a and 164 bof the hydrophobic layer 164. Then, as shown in FIG. 17 d, the organicsemiconductor layer 166 is applied on top of hydrophobic layer 164, andon top of first and second carrier relay layers 163 a and 163 b tocomplete the organic thin film transistor of FIG. 16. The manufacturingmethod of the organic thin film transistor according to FIGS. 17 athrough 17 d has advantages in that it enables the carrier relay layers163 a and 163 b to be readily formed, and accordingly, the organic thinfilm transistor of high quality can be manufactured with low cost.

Turning now to FIG. 18, FIG. 18 is a schematic cross sectional view of aflat panel display device according to the second embodiment of thepresent invention employing the organic thin film transistor of FIG. 16.With reference to FIG. 18, a buffer layer (not shown) made of SiO₂ canbe formed on the substrate 170, if necessary, and as described in theabove, and then the organic thin film transistor (TFT2) is formedthereon. Although FIG. 18 shows, as an example, the organic thin filmtransistor (TFT2) according to the fourth variation among the secondembodiment (FIG. 16), the present invention is not limited thereto.

A passivation layer 173 is formed on the organic thin film transistorTFT2, and a pixel defining layer 175 made of acryl, polyimide, etc. isformed on the passivation layer 173. The drain electrode 161 b isconnected to the light emitting device 180 through a via hole 173 aformed in the passivation layer 173. The light emitting device 180includes a pixel electrode 181 and an opposite electrode 185, and anintermediate layer 183 interposed between the pixel electrode 181 andthe opposite electrode 185, the intermediate layer 183 having at least alight emitting layer. As the display of FIG. 18 has the same basicstructure as the flat panel display device of the first embodiment ofFIG. 10, the details thereof will be omitted.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. An organic thin film transistor, comprising: a source electrode; adrain electrode; an organic semiconductor layer; a gate insulatinglayer; a gate electrode; and a carrier relay layer arranged at leastbetween the organic semiconductor layer and the source electrode orbetween the organic semiconductor layer and the drain electrode, thecarrier relay layer comprising a conductive polymer material.
 2. Theorganic thin film transistor of claim 1, wherein the carrier relay layercomprises a material selected from the group consisting ofpolyethylenedioxythiophene and polyaniline.
 3. The organic thin filmtransistor of claim 1, wherein the carrier relay layer either has workfunction of between a work function of the organic semiconductor layerand a work function of the source electrode, or has work function ofbetween the work function of the organic semiconductor layer and a workfunction of the drain electrode.
 4. The organic thin film transistor ofclaim 1, wherein a thickness of the carrier relay layer is in the rangeof 10 Å to 100 Å.
 5. The organic thin film transistor of claim 1,wherein a resistivity of the carrier relay layer is in the range of 10⁵Ωcm to 10¹⁴ Ωcm.
 6. The organic thin film transistor of claim 1, whereinthe carrier relay layer is arranged corresponding to at least one of thesource electrode and the drain electrode.
 7. The organic thin filmtransistor of claim 6, wherein the carrier relay layer is arranged on atop surface of at least one of the source electrode and the drainelectrode.
 8. The organic thin film transistor of claim 6, wherein thecarrier relay layer is arranged to cover an entire portion of an exposedsurface of at least one of the source electrode and the drain electrode.9. The organic thin film transistor of claim 1, wherein the carrierrelay layer comprises: a first carrier relay layer arranged between theorganic semiconductor layer and the source electrode; and a secondcarrier relay layer arranged between the organic semiconductor layer andthe drain electrode, the first carrier relay layer and the secondcarrier relay layer being spaced apart from each other.
 10. The organicthin film transistor of claim 1, wherein the carrier relay layerarranged between the organic semiconductor layer and the sourceelectrode and the carrier relay layer arranged between the organicsemiconductor layer and the drain electrode are integrally formed. 11.The organic thin film transistor of claim 1, wherein the carrier relaylayer is patterned to correspond to one organic thin film transistor.12. The organic thin film transistor of claim 1, wherein the sourceelectrode or the drain electrode each includes a material selected fromthe group consisting of Ti, Cr, Al and MoW.
 13. The organic thin filmtransistor of claim 1, wherein the organic semiconductor layer includesat least one material selected from the group consisting of pentacene,tetracene, anthracene, naphthalene, flullerene, alpha-6-thiophene,alpha-4-thiophene, oligothiophene, perylene and its derivative, rubreneand its derivative, coronene and its derivative, perylenetetracarboxylic diimide and its derivative, perylene tetracarboxylicdianhydride and its derivative, polythiophene and its derivative,polyparaphenylenevinylene and its derivative, polyparaphenylene and itsderivative, polyfluorene and its derivative, polythiophenevinylene andits derivative, polythiophene-heterocyclic aromatic copolymer and itsderivative, oligoacene of naphthalene and its derivative, naphthalenetetra carboxylic acid diimide and its derivative, oligothiophene ofalpha-5-thiophene and its derivative, phthalocyanines with or withoutmetal and their derivatives, pyromellitic dianhydride and itsderivative, pyromellitic diimide and its derivative, polyalkylthiophene,polythienylenevinylene, alkylfluorene unit, and copolymer ofalkylthiophene.
 14. The organic thin film transistor of claim 1, furthercomprising a hydrophobic layer arranged at least between the organicsemiconductor layer and the source electrode or between the organicsemiconductor layer and the drain electrode.
 15. The organic thin filmtransistor of claim 14, wherein the carrier relay layer is arranged in asame layer as the hydrophobic layer, the carrier relay layer beingadapted to fill in openings in the hydrophobic layer.
 16. The organicthin film transistor of claim 15, wherein the carrier relay layercomprises: a first carrier relay layer arranged between the organicsemiconductor layer and the source electrode; and a second carrier relaylayer arranged between the organic semiconductor layer and the drainelectrode, the first carrier relay layer is arranged to cover a portionof the source electrode closest to the drain electrode, the secondcarrier relay layer is arranged to cover a portion of the drainelectrode closest to the source electrode.
 17. The organic thin filmtransistor of claim 15, the carrier relay layer is arranged on a portionof a top surface of at least one of the source electrode or the drainelectrode.
 18. The organic thin film transistor of claim 15, wherein thecarrier relay layer is arranged covering an entire portion of an exposedsurface of at least one of the source electrode and the drain electrode.19. The organic thin film transistor of claim 14, wherein thehydrophobic layer comprises a surface treatment agent comprising aself-assembled monolayer having one to three of hydrophobic moiety, oneto three of reactive halogen atoms or alkoxy moiety, and silane moiety.20. The organic thin film transistor of claim 19, wherein the surfacetreatment agent of the hydrophobic layer comprises a hydrophobicself-assembled monolayer having trichlorosilanyl moiety ortrialkoxysilanyl moiety at its terminal end.
 21. The organic thin filmtransistor of claim 20, wherein the hydrophobic layer comprisesoctadecyltrichlorosilane.
 22. The organic thin film transistor of claim14, wherein the carrier relay layer comprises a material selected fromthe group consisting of polyethylenedioxythiophene and polyaniline. 23.A method of manufacturing an organic thin film transistor, comprising:forming a conductive polymer material layer on an entire surface of asubstrate; and patterning the conductive polymer material layer by laserablation technology to form a carrier relay layer, the carrier relaylayer being arranged at least between an organic semiconductor layer anda source electrode or between the organic semiconductor layer and adrain electrode.
 24. A method of manufacturing an organic thin filmtransistor, comprising: forming a hydrophobic material layer on anentire surface of a substrate; forming an opening in the hydrophobicmaterial layer; and forming a carrier relay layer in the opening, thecarrier relay layer being arranged at least between an organicsemiconductor layer and a source electrode or between the organicsemiconductor layer and a drain electrode, the carrier relay layercomprising a conductive polymer material.
 25. The method of claim 24,wherein the hydrophobic material layer is produced by a process selectedfrom the group consisting of spin coating and dipping.
 26. The method ofclaim 24, wherein the opening in the hydrophobic material layer isproduced by a laser beam scanning process.
 27. The method of claim 24,further comprising removing remaining conductive polymer material frombetween the source electrode and the drain electrode after the formingthe carrier relay layer in the opening.
 28. The method of claim 27,wherein the remaining conductive polymer material from between thesource electrode and the drain electrode is achieved by a processselected from the group consisting of laser beam, ultraviolet ray, orelectron beam scanning.
 29. A flat panel display device, comprising: asubstrate; and an organic thin film transistor arranged on thesubstrate, the organic thin film transistor comprising: a sourceelectrode, a drain electrode, an organic semiconductor layer, a gateinsulating layer, a gate electrode, and a carrier relay layer arrangedat least between the organic semiconductor layer and the sourceelectrode or between the organic semiconductor layer and the drainelectrode, the carrier relay layer comprises a conductive polymermaterial.
 30. The flat panel display device of claim 29, wherein thecarrier relay layer comprises a material selected from the groupconsisting of polyethylenedioxythiophene and polyaniline.
 31. The flatpanel display device of claim 29, wherein a thickness of the carrierrelay layer is in the range of 10 Å to 100 Å.
 32. The flat panel displaydevice of claim 29, wherein a resistivity of the carrier relay layer isin the range of 10⁵ Ωcm to 10¹⁴ Ωcm.
 33. The flat panel display deviceof claim 29, further comprising a hydrophobic layer arranged between theorganic semiconductor layer and the source electrode or between theorganic semiconductor layer and the drain electrode.
 34. The flat paneldisplay device of claim 33, wherein the carrier relay layer is arrangedon a same level as the hydrophobic layer, the carrier relay layer beingarranged in openings in the hydrophobic layer.
 35. The flat paneldisplay device of claim 33, wherein the hydrophobic layer includes asurface treatment agent having a self-assembled monolayer having one tothree of hydrophobic moiety, one to three of reactive halogen atoms oralkoxy moiety, and silane moiety.
 36. The flat panel display device ofclaim 35, wherein the surface treatment agent of the hydrophobic layercomprises a hydrophobic self-assembled monolayer having trichlorosilanylmoiety or trialkoxysilanyl moiety at its terminal end.
 37. The flatpanel display device of claim 36, wherein the hydrophobic layer includesoctadecyltrichlorosilane.
 38. The flat panel display device of claim 29,further comprising an organic light emitting device electricallyconnected to the organic thin film transistor, the organic lightemitting device includes a first electrode, an organic light emittinglayer, and a second electrode.
 39. The flat panel display device ofclaim 30, the flat panel display device comprising a plurality oforganic thin film transistors, the carrier relay layer being integrallyprovided to the plurality of organic thin film transistors.